[Cryptography] phantom 3g service?

Jon Callas jon at callas.org
Thu Oct 13 17:09:04 EDT 2022

> On Oct 13, 2022, at 12:03, Ray Dillinger <bear at sonic.net> wrote:
> So anyhow, since 3g service has been terminated in my area, I've kept my old phone because it's still fairly useful as a wifi device.  Can't do voice talk or SMS any more since I transferred my phone number, but it still does everything else.
> Thing is, sometimes when I'm walking around, it thinks it sees 3g service.  And I airplane-mode the thing and stick it back in my pocket.
> There are exactly zero carriers in this area who still provide 3g service.
> Are these obsolete stingrays?  Scammers fishing for people who still have old phones and now can't get legit service? Or something else?

I know you said that there are zero carriers.

Nonetheless, I found via <https://www.zdnet.com/home-and-office/networking/3g-is-shutting-down-here-are-the-gadgets-that-still-rely-on-it-do-you-have-one/>:

	• AT&T is the first of the big three, closing its 3G network on February 22, 2022.

	• T-Mobile has pushed its 3G shutdown to July 1, 2022, after initially planning for an October closing in 2021.

	• Sprint, now merged with T-Mobile, will close its 3G network on May 31, 2022.

	• Verizon's 3G network will shut off on December 31, 2022. The carrier has made it clear that "the date will not be extended again."

So it's possible that there is some Verizon tower you're picking up.

I know that when 2G shut down, there was residual service for some time for industrial control devices for some time. I don't remember the details. It's possible that there's something not quite shut down yet -- they stopped consumer service but are keeping something else up until the end of the year.

That article points to this FCC page: <https://www.fcc.gov/consumers/guides/plan-ahead-phase-out-3g-cellular-networks-and-service>.

That page said: "[T-Mobile] also announced it shut down T-Mobile's 3G UMTS network as of July 1, 2022, but has not yet announced a shutdown date for its 2G network." Which is entertaining in the way it interacts with my 2G memories. 

The most likely explanation is that someone has some tower still up for some completely reasonable reason that we'd all facepalm and sigh loudly over. Like industrial control things that are supposed to be phased out six months ago, but supply chain issues put the kibosh on their intended schedule.

If you're really curious, you could run software on something with an SDR and check it out. My team at EFF made <https://github.com/EFForg/crocodilehunter>, which sadly is LTE-only, but could be modified to do 3G spectrum by an enterprising person. (Yes, I am smiling as I type this.)


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